The present invention relates to improved particulates and methods of using such particulates in subterranean applications. More particularly, the present invention relates to composite particulates and their use in subterranean applications such as production enhancement and completion.
Particulates are used in a variety of operations and treatments performed in oil and gas wells. Such operations and treatments include, but are not limited to, production stimulation operations such as fracturing and well completion operations such as gravel packing.
An example of a production stimulation operation using a servicing fluid having particles suspended therein is hydraulic fracturing. That is, a type of servicing fluid, referred to in the art as a fracturing fluid, is pumped through a well bore into a subterranean zone to be stimulated at a rate and pressure such that fractures are formed and extended into the subterranean zone. The fracture or fractures may be horizontal or vertical, with the latter usually predominating, and with the tendency toward vertical fractures generally increasing with the depth of the formation being fractured. Generally, fracturing fluids are viscous fluids in the form of gels, emulsions, or foams. The particulate materials used in these operations are often referred to as proppant. The proppant is deposited in the fracture and functions, inter alia, to maintain the integrity of the fracture open while maintaining conductive channels through which such produced fluids can flow upon completion of the fracturing treatment and release of the attendant hydraulic pressure.
Particulates also are used in well completion operations such as gravel packing. Gravel packing treatments are used, inter alia, to reduce the migration of unconsolidated formation particulates into the well bore. In gravel packing operations, particulates, often referred to in the art as gravel, are carried to a well bore in a subterranean producing zone by a servicing fluid that acts as a gravel carrier fluid. That is, the particulates are suspended in a carrier fluid, which may be and usually is viscosified, and the carrier fluid is pumped into a well bore in which the gravel pack is to be placed. As the particulates are placed in or near the zone, the carrier fluid leaks off into the subterranean zone and/or is returned to the surface. The resultant gravel pack acts as a sort of filter to prevent the production of the formation solids with the produced fluids. Traditional gravel pack operations involve placing a gravel pack screen in the well bore before packing the surrounding annulus between the screen and the well bore with gravel. The gravel pack screen is generally a filter assembly used to support and retain the gravel placed during the gravel pack operation. A wide range of sizes and screen configurations is available to suit the characteristics of a well bore, the production fluid, and any particulates in the subterranean formation. Gravel packs are used, among other reasons, to stabilize the formation while causing minimal impairment to well productivity.
Also, as more wells are being drilled in deep water and in high temperature zones, gravel packing in long, open horizontal well bores is becoming more prevalent. Completion operations in these wells generally involve the use of reduced-specific gravity particulates that are resistant to degradation in the presence of hostile conditions such as high temperatures and subterranean treatment chemicals. Using lightweight particulates may enhance the complete packing of the well bore annulus between the well bore and the sand screens, and possibly minimize the potential of particulate settling, leaving behind void spaces on top of the gravel pack. Void spaces on top of a gravel pack may be problematic as formation sand or fines often fill such voids during production, which may result in a significant reduction of produced fluids from the well. Erosion of the screen could also occur at a particular location where production flow rate is concentrated at one point on the screen, which in turn allows the gravel or formation materials to produce along with the production fluids.
In some situations, hydraulic fracturing and gravel packing operations may be combined into a single treatment. Such treatments are often referred to as “frac pack” operations. In some cases, the treatments are completed with a gravel pack screen assembly in place with the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In this situation, the hydraulic fracturing treatment ends in a screen-out condition, creating an annular gravel pack between the screen and casing. In other cases, the fracturing treatment may be performed prior to installing the screen and placing a gravel pack.
Traditional high-strength particulates used in fracturing applications often exhibit too high of a specific gravity to be suspended in lower viscosity fluids. Lower viscosity fluids are desirable because the viscosifiers and crosslinkers used to create them are often expensive. Moreover, viscosifier tends to build up on the walls of the formation in the form of a filter cake that may black the production of fluids once it is desirable to place the formation on production. Moreover, residue of viscosifiers used in subterranean applications often remains on the particulates transported in the viscosified fluid and may reduce the conductivity of packs made from such particulates. While low specific gravity particulates are suitable for use in lower viscosity fluids, these low specific gravity particulates generally are not able to withstand significant closure stresses over time at elevated subterranean temperatures. Examples of such particulates include walnut hulls and thermoplastic materials, including polyolefins, polystyrene divinylbenzene, polyfluorocarbons, polyethers etherketones and polyamide imides, that tend to soften and deform under stress when exposed to temperatures above about 150° F.